<h1 id="utah-congressional-districts">2020 Utah Congressional
Districts</h1>
<h2 id="redistricting-requirements">Redistricting requirements</h2>
<p>In Utah, districts must, under <a
href="https://le.utah.gov/xcode/Title20A/Chapter20/20A-20-S302.html">legislation
code 20A-20-302</a>:</p>
<ol type="1">
<li>have a total population deviation of less than 1% (where total
population deviation is calculated by adding together the percentage
deviation of both the most populous and least populous districts from
the average, or “ideal,” district)</li>
<li>not be drawn with race used as a predominant factor</li>
<li>be contiguous and reasonably compact</li>
<li>to the extent practicable
<ol type="a">
<li>preserve communities of interest</li>
<li>follow natural, geographic, or man-made features, boundaries, or
barriers</li>
<li>preserve cores of prior districts</li>
<li>minimize the division of municipalities and counties across multiple
districts</li>
<li>achieve boundary agreement among different types of districts</li>
<li>prohibit the purposeful or undue favoring or disfavoring of
incumbents, candidates or prospective candidates, and political
parties</li>
</ol></li>
</ol>
<h3 id="algorithmic-constraints">Algorithmic Constraints</h3>
<p>We enforce a maximum population deviation of 0.5% (which ensures that
the total population deviation as defined by Utah legislation does not
exceed 1%). We constrain the number of “pseudo-county” divisions (see
below for an explanation of pseudo-county). We perform cores-based
simulations, thereby preserving cores of prior districts.</p>
<h2 id="data-sources">Data Sources</h2>
<p>Data for Utah comes from the ALARM Project’s <a
href="https://alarm-redist.github.io/posts/2021-08-10-census-2020/">2020
Redistricting Data Files</a>. Data for the 2021 Utah Congressional
adopted plans come from Utah Legislative Redistricting Committee’s <a
href="https://citygate.utleg.gov/legdistricting/utah/comment_links#">MyDistricting
site</a></p>
<h2 id="pre-processing-notes">Pre-processing Notes</h2>
<p>We create pseudo-counties by splitting counties with a total
population higher than the target district population into
county-municipality combinations (in the end, this affects only Salt
Lake County, which has a total population well above 1 million). To
preserve the cores of prior districts, we merge all precincts which are
more than two precincts away from a district border under the 2010
plan.</p>
<h2 id="simulation-notes">Simulation Notes</h2>
<p>We sample 6,000 districting plans for Utah across two independent
runs of the SMC algorithm. To balance county and municipality splits, we
create pseudo-counties as described above.</p>
<h2 id="contents">Contents</h2>
<ul>
<li><code>UT_cd_2020_stats.csv</code> contains summary statistics on the
sampled redistricting plans</li>
<li><code>UT_cd_2020_plans.rds</code> is a compressed
<code>redist_plans</code> object, which contains the matrix of
precinct/block assignments and may be used for further analysis.</li>
<li><code>UT_cd_2020_map.rds</code> is a compressed
<code>redist_map</code> object, which contains the precinct/block
shapefile and demographic data.</li>
</ul>
<p>Both the <code>redist_plans</code> and <code>redist_map</code> object
are intended to be used with the <a
href="https://alarm-redist.github.io/redist/">redist package</a>.</p>
<h3 id="codebook-for-summary-statistics">Codebook for summary
statistics</h3>
<ul>
<li><code>draw</code>: unique identifier for each sample. Non-numeric
draw names are real-world plans, e.g., <code>cd_2010</code> for an
enacted 2010 plan.</li>
<li><code>district</code>: a district identifier. District numbers
roughly match those in the enacted plan, but the correspondence is not
perfect.</li>
<li><code>chain</code>: a number identifying the run of the
redistricting algorithm used to produce this draw. Used for diagnostic
purposes.</li>
<li><code>pop_overlap</code>: a number indicating the fraction of people
in this plan who reside in the same-numbered district in the enacted
plan.</li>
<li><code>total_pop</code>: the total population of each district.</li>
<li><code>total_vap</code>: the total voting-aged population of each
district.</li>
<li><code>pop_*</code>, <code>vap_*</code>: total (voting-aged)
population within racial and ethnic groups for each district. Variable
codes documented <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>plan_dev</code>: the maximum population deviation among
districts in the plan. Computed as
<code>max(abs(distr_pop - target_pop)/target_pop)</code>.</li>
<li><code>comp_edge</code>: compactness, as measured by the fraction of
internal edges kept. Higher values indicate more compactness.</li>
<li><code>comp_polsby</code>: compactness, as measured by the
Polsby-Popper score. Higher values indicate more compactness.</li>
<li><code>county_splits</code>: the number of counties which belong to
more than one district.</li>
<li><code>muni_splits</code>: the number of Census Designated Places
which belong to more than one district.</li>
<li><code>*_##_dem_*</code>, <code>*_##_rep_*</code>: vote counts for
statewide Democratic and Republican candidates in a certain election.
More information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>adv_##</code>, <code>arv_##</code>: average vote counts for
statewide Democratic and Republican candidates in a certain year. More
information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>ndv</code>, <code>nrv</code>: averages of the
<code>adv_##</code> and <code>arv_##</code> variables across all
available elections.</li>
<li><code>ndshare</code>: normal Democratic share, computed as
<code>ndv / (ndv + nrv)</code></li>
<li><code>e_dvs</code>: average Democratic vote share, computed as the
average of the Democratic vote share when first scored under each
statewide election.</li>
<li><code>pr_dem</code>: probability seat is represented by a Democrat;
calculated as the fraction of statewide elections under which the
district had a majority Democratic share.</li>
<li><code>e_dem</code>: expected number of Democratic seats for the
plan; equivalent to summing the <code>pr_dem</code> values across
districts</li>
<li><code>pbias</code>: partisan bias at 50% vote share, averaged across
all available elections. Positive values indicate Republican bias.</li>
<li><code>egap</code>: the efficiency gap, averaged across all available
elections. Positive values indicate Republican bias.</li>
</ul>
